The safety of occupants of automobiles during a collision can improve with the installation of impact absorbing components. Such components and members absorb the energy of the impact and may alternatively be referred to as energy absorbing components or members in the structure of the automobile. The official gazette of Japanese Patent No. 3,313,999 discloses an energy absorbing component with a hollow double wall structure, produced by blow molding of thermoplastics, forming recessed ribs from the front surface wall and the rear surface wall with the top end parts thereof bonded with each other so as to be integrated for improving the energy absorbing property, and the official gazette of Japanese Patent Application Laid Open (JP-A) No. 2002-187508 discloses one comprising an interlocking rib for integrally linking a plurality of recessed ribs for improving the energy absorbing property.
This kind of energy absorbing member is designed to be provided inside a vehicle structural member such as a door and a body side panel. It has been found that a sufficient shock absorbing property is not obtained by merely linking a plurality of the recessed ribs integrally as shown in the official gazette of Japanese Patent Application Laid Open (JP-A) No. 2002-187508.
Moreover, according to the energy absorbing member for a vehicle as disclosed in the official gazette of Japanese Patent No. 3,313,999 produced by forming recessed ribs from the front surface wall and the rear surface wall with the top end parts thereof bonded with each other so as to be integrated, it is pointed out that although the shock absorbing property with respect to the stress by the impact is high, in the case the stress by the impact is applied continuously, the recessed ribs buckle so that the energy absorbing property is deteriorated remarkably so that the intended shock absorbing property is not obtained.
Furthermore, since the welded surface produced by forming recessed ribs from the front surface wall and the rear surface wall and welding the top end parts with each other in the blow molding process is formed by pressuring a parison in a molten state by a mold, the resin in the molten state is pushed out to the outer circumference of the bonding part so as to generate a puddle as shown in FIG. 11. The marks a′, b′ denote recessed ribs, c′ a bonding part, and d′ a resin puddle swelling to the outside of the bonding part c′. Thereby, a notch part is formed or the wall thickness of the recessed rib becomes uneven so that the shock absorbing performance of the energy absorbing member is lowered, and thus a desired shock absorbing effect cannot be obtained.
Accordingly, it is desirable to provide an energy absorbing member for a vehicle made of thermoplastics, capable of providing excellent shock absorbing property, and being formed integrally by blow molding.